How to show usage of static methods UML Class Diagram

Question

How do i show the use of static methods in a UML class diagram?

class A{
    public static void test(){
    }
}

class B{
    public void b(){
    A.test();
    }
}

How would a class diagram look like, which shows the relationship? UML 2.0 would be prepared, if there is a difference.

Jagatai

Answer 1

To show a static method you underline the name of the static method - have a look here for more detailed info.

As for navigating that relationship; class B is dependent on the existance of class A. We can say that class B has a "usage dependency" on class A

class B ----uses----> class A

Hope this helps.

Antemundane

Are you sure its a dependency relationship and not an association? – Jagatai

An association is a relationship between two (or more) types that are linked by an instance(s). So for ClassB to have an association with ClassA it needs to have a reference to it, perhaps via a property or field. But since that is not the case in your example, I would say that you have a dependency and not an association. I think that the definition in this link shows that you have a dependency. – Antemundane

Answer 2

To show static methods and attributes you underline them in a UML class diagram: see UML Distilled p.66 or section 7.3.19 (Feature) of the UML Superstructure specification:

Static features are underlined.

To show the relationship between classes B and A (where B only uses static methods in A), you use a dependency, not an association. Associations are always between instances of the classes at each end, as in section 7.3.3 (Association) of the UML Superstructure spec:

An association specifies a semantic relationship that can occur between typed instances.

But class B is dependent on class A, as in section 7.3.12 of the spec:

A dependency is a relationship that signifies that a single or a set of model elements requires other model elements for their specification or implementation.

It is probably worth clarifying the nature of the dependency with a stereotype. You could use a use stereotype, but that's very general and actually encompasses standard associations between instances (though you obviously normally use associations to explicitly show them). As Fowler says in UML Distilled,

Many UML relationships imply a dependency. The navigable association from Order to Customer [in one of his examples...] means that Order is dependent on Customer.

There seems to be no standard on what stereotype to use. I've used usesStatically to be clear on the nature of the dependency; that is

B --usesStatically--> A

(If, alternatively, class B had an instance of A as a static field, I'd use something like B--containsStatically--> A if I'm representing B explicitly in the class diagram; otherwise just have an underlined static attribute of type A in B.)

Thereinafter

I thought @RobertMS's answer was worth expanding on but have put this as a community wiki answer since it does 'just' explain some nuances of his answer (and link to more 'official' references). – Lark

What does Static features are underlined mean? Could somebody show me an example? – Trifle

@Trifle It means what it says; i.e.., to show a field or method is static you underline its name in the class diagram. – Lark

Am I the only one who read that as "undefined"? – Doff

Answer 3

@RobertMS is right.

Another alternative, is to use stereotypes:

..............................................................
....+----------------------------------------------------+....
....|                StringUtilityClass                  |....
....+----------------------------------------------------+....
....| [+] void: lowerCase()              <<non virtual>> |....
....| [+] void: upperCase()              <<non virtual>> |....
....| [+] String: toString()                <<override>> |....
....+----------------------------------------------------+....
....| [+] String: LowerCaseCopy(String Value) <<static>> |....
....| [+] String: UpperCaseCopy(String Value) <<static>> |....
....| [+] String: ReverseCopy(String Value)   <<static>> |....
....+----------------------------------------------------+....
..............................................................

Note Some programming languages best practices, especially those with C case-sensitive syntax, capitalize static functions, and leave in camel-lowercase the rest of functions.

Cheers.

Tarr